Metal Salt-Containing Composition, Substrate, Manufacturing Method of Substrate

ABSTRACT

An object of the present invention is to provide a metal salt-containing composition which is applicable to many metal source materials, and can be used for forming a compact and uniform metal oxide film comparable to those formed according to a sputtering method, as well as to provide a substrate having a metal complex film on the surface thereof obtained using the metal salt-containing composition, and a substrate having a metal complex film on the surface thereof obtained by further heating the substrate. Moreover, another object of the present invention is to provide a method for manufacturing a substrate having such a metal complex film on the surface thereof. 
     According to the present invention, a metal salt-containing composition containing a metal salt, a polyvalent carboxylic acid having a cis-form structure, and a solvent, in which: the molar ratio of the polyvalent carboxylic acid to the metal salt is not less than 0.5 and not more than 4.0; the moisture content of the composition is not less than 0.05% by weight is used in an application method to apply on a substrate. Thereafter, a two-step heat treatment is carried out.

TECHNICAL FIELD

The present invention relates to a metal salt-containing composition foruse in forming a metal oxide film on a substrate, and more specificallyto a metal salt-containing composition containing a metal salt, apolyvalent carboxylic acid having a cis-form structure, and a solvent(which may include water). In addition, the present invention relates toa metal complex film obtained using such a metal salt-containingcomposition and a substrate having a metal oxide thin film formed on thesurface thereof, and a method for manufacturing a substrate having ametal oxide thin film formed on the surface thereof.

BACKGROUND ART

As techniques for coating a variety of metal compound thin films on thesurface of various types of substrates, a sputtering method, gas phasemethods such as a vacuum deposition method, a sol-gel method, solutionmethods by thermal decomposition etc., of an organic acid metal salt oran organic metal complex have been known.

First, the sputtering method enables a compact and homogenous metalcompound thin film to be formed on the surface of a substrate, and hasbeen predominantly employed for the present. However, in the case inwhich the surface of the substrate has a complicated shape, it isimpossible to form a metal oxide thin film on recessed portions.

Next, the gas phase methods are procedures that require high costs sinceit is necessary to prepare a thin film under a high-vacuum atmosphere.In addition, there is a problem of difficulty in obtaining a metalcompound thin film having high crystallinity. Further, similarly to thesputtering method, to form a metal oxide thin film on recessed portionsis impossible when the surface of the substrate has a complicated shape.

Subsequently, the sol-gel method requires time-consuming hydrolysis andpolycondensation steps of the source material such as a metal alkoxide,in addition, there is a problem of not capable of readily applying whengelated due to difficulty in controlling the gelation reaction.

Finally, the solution method in which an organic acid metal salt or anorganic metal complex is thermally decomposed enables a metal oxide thinfilm to be formed under an ordinary pressure even on the surface havinga complicated shape. This method is a comparatively simple method sincea thin film can be formed by merely carrying out thermal decompositionin the air under an ordinary pressure after an organic acid metal saltor an organic metal complex to be a precursor is dissolved in an organicsolvent, and the solution is applied on the substrate with spin coatingor the like. However, as in the sputtering method, formation of acompact and homogenous metal oxide thin film is difficult, and there isa problem of applicability to only limited source materials such asacetic acid salts, alkoxides and the like.

CITATION LIST Patent Literature

PTL 1: Japanese Patent-Laid-open Publication No. 2003-267705

PTL 2: Japanese Patent-Laid-open Publication No. H09-012976

PTL 3: Japanese Patent-Laid-open Publication No. S64-11977

PTL 4: Japanese Patent-Laid-open Publication No. H11-256342

Nonpatent Literature

NPL 1: “Sol-gel Method and Organic-inorganic Hybrid Material” TechnicalInformation Society, Aug. 31, 2007, P. 3-17

SUMMARY OF INVENTION Technical Problem

In the prior arts described above, a uniform metal oxide thin film canbe formed on a substrate only when a certain metal salt such as analkoxide, acetic acid salt or the like is used. Therefore, a method inwhich more kinds of metal source materials can be used, and enables acompact and uniform metal oxide thin film to be readily produced hasbeen demanded.

An object of the present invention is to provide a metal salt-containingcomposition which is applicable to many metal source materials, and canbe used for forming a compact and uniform metal oxide film comparable tothose formed according to the sputtering method. In addition, anotherobject of the present invention is to provide a substrate having a metalcomplex film on the surface thereof obtained using such a metalsalt-containing composition, and a substrate having a metal complex filmon the surface thereof obtained by further heating such a substrate.Moreover, still another object of the present invention is to provide amethod for manufacturing a substrate having such a metal complex film onthe surface thereof.

Solution to Problem

The present inventors thoroughly investigated on a method of forming ametal oxide thin film on a substrate composed of a material such as aglass, silicon, metal or ceramic by an application method, andconsequently found that a compact and homogenous metal oxide thin filmcan be formed on a substrate when a metal compound to be a metal sourcematerial is mixed at a specified rate with a polyvalent carboxylic acidhaving at least one cis-form structural site, and a solution is preparedby dissolving the mixture in a solvent including water (metalsalt-containing composition) is provided as an application liquid.Accordingly, the present invention was accomplished.

Specifically, one aspect of the present invention relates to

a metal salt-containing composition comprising

a metal salt,

a polyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and

a solvent, wherein:

the molar ratio of the polyvalent carboxylic acid to the metal salt isnot less than 0.5 and not more than 4.0;

the moisture content of the composition is not less than 0.05% byweight; and

the composition is used for forming a metal oxide thin film by applyingon a substrate followed by baking.

Still further, another aspect of the present invention relates to

a substrate having a metal complex film formed on the surface thereof,the metal complex film being obtained by:

applying on the surface of the substrate a solution comprising

a metal salt,

a polyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and

a solvent,

the molar ratio of the polyvalent carboxylic acid to the metal saltbeing not less than 0.5 and not more than 4.0, and the moisture contentof the solution being not less than 0.05% by weight; and

drying by heating at a temperature of not lower than 100° C. and nothigher than 250° C.

Additionally, still another aspect of the present invention relates to

a method for manufacturing a substrate having an oxidized metal thinfilm formed on the surface thereof, the method comprising:

an application step of applying on the surface of the substrate asolution comprising

a metal salt,

a polyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and

a solvent,

the molar ratio of the polyvalent carboxylic acid to the metal saltbeing not less than 0.5 and not more than 4.0, and the moisture contentof the solution being not less than 0.05% by weight;

a primary heating step of drying by heating the solution at atemperature of not lower than 100° C. and not higher 250° C.; and

a secondary heating step of further heating the substrate after theprimary heating step at a temperature no lower than 400° C.

The cis-form structural site is identified to be necessary sinceuniformity of the metal oxide thin film obtained on the substrate wasdeteriorated when a polyvalent carboxylic acid not having a cis-formstructural site was used. It is to be noted that C═C bond of thepolyvalent carboxylic acid in the present invention may be acarbon-carbon double bond that composes an aromatic ring.

Herein, it is necessary that the solution containing a metal salt, apolyvalent carboxylic acid having a cis-form structure, and a solvent(application liquid) has a moisture content of not less than 0.05% byweight as a solution. The metal salt may be a hydrate, and the solventmay include water. The moisture of not less than 0.05% by weightcontained in the entirety of the application liquid is sufficient.

When the amount of the polyvalent carboxylic acid added relative to theamount of the metal salt is too small, uniformity of the metal oxidethin film is deteriorated. Whereas, when the amount is too large, theamount of organic matter in the film on the substrate becomes too largein baking; therefore, the uniformity of the film is deteriorated.Accordingly, the molar ratio of the polyvalent carboxylic acid to themetal salt is preferably not less than 0.5 and not more than 4.0, andmore preferably not less than 0.8 and not more than 2.0.

The content (concentration) of the metal salt in the metalsalt-containing composition (application liquid) is not particularlylimited since it is sufficient as long as the metal salt is dissolved inthe solvent, and may be adjusted ad libitum depending on the intendedfilm thickness of the metal oxide thin film. In light of attaining apractically applicable film thickness, the content of the metal salt ispreferably not less than 0.005 mol/L and not more than 1 mol/L.

The metal salt-containing composition is prepared into an applicationliquid and can be applied on the substrate by a well-known procedure inapplication methods carried out using a spray, spin coating, screenprinting, an applicator, a bar coater, a roll coater, a gravure coateror the like. In this process, the application liquid is preferablyapplied such that a uniform film thickness is attained in theapplication to meet the characteristics of the application procedure.

Although a solvent which can be used in the present invention is notparticularly limited as long as the metal salt and the polyvalentcarboxylic acid can be stably dissolved, for example, water, methanol,ethanol, ethylene glycol, propylene glycol, 1,3-propanediol,1,3-butanediol, 3-methoxymethylbutanol, N-methylpyrrolidone, terpineol,and the like may be exemplified.

The metal salt is preferably at least one salt selected from the groupconsisting of Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Nb, Ta, Cr, W, Fe, Ni, Cu,Ag, Zn, Al, Ga, In, Sn and Sb.

The metal salt is preferably at least one metal salt selected from thegroup consisting of a nitric acid salt, a sulfuric acid salt, acarboxylic acid salt, a halide, an alkoxide and an acetyl acetone salt.

The polyvalent carboxylic acid is preferably at least one selected fromthe group consisting of maleic acid, citraconic acid, phthalic acid andtrimellitic acid. In view of a low decomposition temperature, andability to provide a more compact metal oxide thin film, maleic acid isparticularly preferred. Also, the polyvalent carboxylic acid may begenerated in the solution by using an anhydride of the polyvalentcarboxylic acid with a solvent including water.

In addition, another aspect of the present invention relates to asubstrate having a metal oxide film formed on the surface thereof from

a substrate having a metal complex film formed on the surface thereof,the metal complex film being obtained by:

applying on the surface of the substrate a solution comprising

a metal salt,

a polyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and

a solvent,

the molar ratio of the polyvalent carboxylic acid to the metal saltbeing not less than 0.5 and not more than 4.0, and the moisture contentof the solution being not less than 0.05% by weight; and

drying by heating at a temperature of not lower than 100° C. and nothigher than 250° C., and

further heating thus obtained substrate at a temperature of not lowerthan 400° C.

The aforementioned objects, other objects, features, and advantages ofthe present invention are clarified by the following detaileddescription of preferred embodiments with reference to accompanyingdrawings.

Advantageous Effects of Invention

According to the present invention, various types of metal sourcematerials are adopted to an application method, and thus production of amore compact and uniform metal oxide thin film than those obtainedaccording to conventional application methods is enabled on a substrateat low costs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an SEM photograph illustrating the surface of the substrateafter primary heating of Example 1.

FIG. 2 shows an SEM photograph illustrating the surface of the substrateafter primary heating of Comparative Example 1.

FIG. 3 shows an SEM photograph illustrating the surface of the substrateafter primary heating of Comparative Example 4.

FIG. 4 shows an SEM photograph illustrating the surface of the substrateafter primary heating of Comparative Example 5.

FIG. 5 shows an SEM photograph illustrating the surface of the substrateafter secondary heating of Example 1.

FIG. 6 shows an SEM photograph illustrating the surface of the substrateafter secondary heating of Comparative Example 1.

FIG. 7 shows an SEM photograph illustrating the surface of the substrateafter secondary heating of Comparative Example 4.

FIG. 8 shows an SEM photograph illustrating the surface of the substrateafter secondary heating of Comparative Example 5.

FIG. 9 shows an SEM photograph illustrating the surface of the substrateof Comparative Example 14.

FIG. 10 shows an SEM photograph illustrating the surface of thesubstrate of Comparative Example 15.

DESCRIPTION OF EMBODIMENTS

Hereinafter, modes for carrying out the present invention are explainedwith appropriate reference to accompanying drawings.

EXAMPLE 1

Zinc nitrate hexahydrate in an amount of 0.8924 g (0.003 mol), 0.5221 g(0.0045 mol) of maleic acid and 7.96 g of 3-methoxy-3-methyl-1-butanol(MMB, product name: Solfit Fine Grade, manufactured by Kuraray Co.,Ltd.) were mixed, and the mixture was subjected to an ultrasonictreatment in an ultrasonic bath for 10 to 30 min to prepare a solutionhaving a metal salt content of 0.3 mol/L (metal salt-containingcomposition), and the properties were identified.

Next, after the prepared solution was spin coated at 2,000 rpm for 30sec on a slide glass (glass substrate), primary heating was carried outin an air dry furnace at 150° C. for 10 min. Thereafter, the appearanceof the metal complex thin film formed on the surface of the substratewas observed. Moreover, after the substrate was subjected to secondaryheating (baking) in the air in an electric muffle furnace at 500° C. for30 min, the appearance of the metal oxide thin film formed on thesurface of the substrate was observed. It is to be noted that the metalcomplex thin film and the metal oxide thin film formed on the surface ofthe substrate had a film thickness falling within the range of not lessthan 0.03 μm and not more than 0.05 μm.

EXAMPLES 2 TO 46

Similar operations to those in Example 1 were carried out except thatthe metal salt, the polyvalent carboxylic acid, the molar ratio, and thesolvent were changed. In addition, the appearances of the surface of thesubstrate after the primary heating and the secondary heating wereobserved. The compositions and results of observation in Examples 1 to46 are shown in Table 1.

In Table 1, the molar ratio means a molar ratio of the polyvalentcarboxylic acid to the metal salt. Appearance 1 means the appearance ofthe metal complex thin film after the primary heating, and Appearance 2means the appearance of the metal oxide thin film after the secondaryheating. Crack means the presence or absence of crack on the metal oxidethin film after the secondary heating. Furthermore, in Examples 43 to46, a mixture of two kinds of the metal nitric acid salts in equimolaramounts was used.

Also, 3-methoxy-3-methyl-1-butanol (MMB) in Table 1 and Table 2described later contains about 0.05% by weight of water.

TABLE 1 Amount of moisture in solution Polyvalent Molar (% by LiquidExample Metal Anion carboxylic acid ratio Solvent weight) propertyAppearance 1 Appearance 2 Crack 1 Zn NO₃ ⁻ maleic acid 1.5 MMB 4transparent uniform uniform Absent 2 MMB/water = 12.5 90/10 (wt %) 3phthalic acid MMB 4 4 trimellitic acid 5 citraconic acid 6 maleicanhydride MMB/water = 12.5 90/10 (wt %) 7 maleic acid water 86 8 2 84 93 81 10 1.5 methanol 4 11 ethanol 12 ethylene glycol 13 propylene glycol14 n-methyl- pyrrolidone 15 CH₃COO⁻ water 86 16 acetyl 17 acetone Cl 18Br MMB 19 butoxide 0.08 20 Ti Isopropoxide 21 Mg NO₃ ⁻ 22 Ca 23 Sr 24 Ba25 Y 26 Ti 27 Zr butoxide 28 Hf NO₃ ⁻ 29 Nb 30 Ta 31 Cr 32 W 33 Fe 34 Ni35 Cu 36 Ag 37 Al 38 Ga 39 In 40 Si ethoxide 41 Sn NO₃ ⁻ 42 Sb 43 In +Sn 44 In + Zn 45 Sn + Zn 46 Sb + Sn

COMPARATIVE EXAMPLES 1 TO 13

Similar operations to those in Example 1 were carried out except thatzinc nitrate was used as the metal salt, and the type and the amount ofthe carboxylic acid etc., were changed. In addition, the observation wascarried out similarly to Example 1. The results are shown in Table 2. Itis to be noted that the metal complex thin film and the metal oxide thinfilm formed on the surface of the substrate had a film thickness fallingwithin the range of not less than 0.05 μm and not more than 1 μm.

TABLE 2 Amount of Comparative Molar moisture in Liquid Example MetalAnion Carboxylic acid etc. ratio Solvent solution (wt %) propertyAppearance 1 Appearance 2 1 Zn NO₃ ⁻ None 0 MMB 4 transparent generationof generation of turbidity and turbidity and crack crack 2 maleic acid0.2 nonuniformity nonuniformity 3 5 found found 4 fumaric acid 1.5generation of generation of 5 succinic acid turbidity and turbidity and6 succinimide crack crack 7 isophthalic acid insoluble failure infailure in 8 terephthalic acid application application 9 pyromelliticacid gelated 10 citric acid transparent generation of generation ofturbidity and turbidity and crack crack 11 oxalic acid gelated failurein failure in 12 diethanolamine application application 13 acetylacetone transparent generation of generation of turbidity and turbidityand crack crack

In Examples 1 to 46, the polyvalent carboxylic acid having a cis-formstructure of —C(COOH)═C(COOH)— was mixed with 1.5 times the metal saltin a molar ratio and dissolved in the solvent; however, in any of theExamples, the properties of the solution (i.e., metal salt-containingcomposition) exhibited a transparent liquid. Therefore, uniformapplication by spin coating on a slide glass was enabled. In addition,the metal complex thin film formed on the substrate after the primarydrying was uniform, and neither turbidity nor crack was found.

On the other hand, in Comparative Examples 7 to 9, 11 and 12, eventhough the metal salt, the carboxylic acid etc., were mixed with thesolvent, dissolution failed, or immediately gelated to result in failurein applying on the slide glass by spin coating. Moreover, although atransparent solution was obtained in other Comparative Examples,observation of the substrate after the primary heating revealed that thethin film got turbid, or the surface exhibited nonuniformity andgeneration of crack. Such a state was maintained on the substrate alsoafter the secondary heating.

(Metal Complex Formed After Primary Drying)

Zinc nitrate hexahydrate in an amount of 0.8924 g (0.003 mol), 0.5221 g(0.0045 mol) of maleic acid, 7 g of methanol and 1 g of water weremixed, and the mixture was subjected to a treatment in an ultrasonicbath for 10 to 30 min to allow for dissolution. Thereafter, the solventwas evaporated to give blight white powders. When the powders wereheated at 150° C. for 10 min, the color of the powders changed intoyellowish brown.

The yellowish brown powders were dissolved in a CDCl₃ solution, andsubjected to determination on a ¹H-NMR spectrum but no peak wasrevealed. On the other hand, the powders were dissolved in a D₂Osolution, and similarly subjected to determination on a ¹H-NMR spectrum.Thus observed spectrum exhibited a peak at a position suggestingchemical shift, showing a shift to a lower magnetic field as comparedwith the NMR spectrum of maleic acid alone.

When maleic acid not bound by zinc remains, the maleic acid is dissolvedin the CDCl₃ solution; therefore, the sample prepared by dissolving theaforementioned yellowish brown powders in the CDCl₃ solution should haveexhibited the NMR spectrum in which observation of maleic acid wasindicated. However, since maleic acid was not observed in the NMRspectrum, taking into consideration from the state of chemical shiftindicated in the spectrum obtained when dissolved in the D₂O solution,the powders were presumed to be a complex of zinc and maleic acid at aratio of 1:1.

In addition, also a solution prepared by dissolving a bivalent metalsalt other than zinc and a polyvalent carboxylic acid other than maleicacid having a cis-form structure of —C(COOH)═C(COOH)— was subjected to astudy similarly to those described above, and consequently chemicalshift presumed to indicate a complex of metal and maleic acid at a ratioof 1:1 was observed in the NMR spectrum. Therefore, it was supposed thata thin film of the metal complex represented by the following formulawas formed on the surface of the substrate after the primary dryingstep. It should be noted that M is a bivalent metal in the followingformula.

(Electron Micrograph of the Surface of the Substrate)

A scanning electron microscope (SEM) photograph of the surface of thesubstrate (surface on which the application liquid was spin coated)after the primary heating of the substrate produced in Example 1 isshown in FIG. 1. In addition, SEM photographs of the surface of thesubstrate (surface on which the application liquid was spin coated)after the primary heating of the substrates produced in ComparativeExamples 1, 4 and 5 are shown in FIGS. 2, 3 and 4, respectively.

The surface of the substrate of Example 1 was uniform, and formation ofa compact metal complex thin film was verified. On the other hand,formation of aggregates and formation of a poorly compact film wereverified on the substrate of Comparative Example 1; formation of theaggregates was verified on the substrate of Comparative Example 4; andformation of aggregates was verified and formation of a uniform andcompact film failed on the substrate of Comparative Example 5.

Furthermore, a scanning electron microscope (SEM) photograph of thesurface of the substrate (surface on which the application liquid wasspin coated) after the secondary heating of the substrate produced inExample 1 is shown in FIG. 5. In addition, SEM photographs of thesurface of the substrate (surface on which the application liquid wasspin coated) after the secondary heating of the substrates produced inComparative Examples 1, 4 and 5 are shown in FIGS. 6, 7 and 8,respectively.

The surface of the substrate of Example 1 was uniform, and formation ofa compact metal oxide thin film was verified. On the other hand, thesubstrates of Comparative Examples 1, 4 and 5 were nonuniform, and manycracks were found, not suggesting a practically applicable value as asubstrate on which a metal oxide thin film was formed.

(Secondary Heating Temperature)

The secondary heating had to be carried out at a temperature of no lowerthan 400° C., and a temperature of 500° C. was employed in the foregoingExamples. The upper limit temperature of the secondary heating isdetermined preferably depending on the heatproof temperature of thesubstrate. For example, in the case of substrates having a heatprooftemperature lower than slide glasses, the secondary is heatingpreferably carried out at a temperature around 400° C., whereas in thecase of substrates having a heatproof temperature higher than slideglasses to the contrary, the secondary heating can be carried out at ahigh temperature approximate to the heatproof temperature.

(Effects of Primary Heating) COMPARATIVE EXAMPLE 14

Entirely similar operations to those in Example 1 were carried outexcept that the substrate was heated (baked) in the air in an electricmuffle furnace at 500° C. for 30 min without heating in the air dryfurnace at 150° C. for 10 min, after the prepared solution was spincoated on a slide glass. Then, the appearance of the metal oxide thinfilm formed on the surface of the substrate was observed. In otherwords, the primary heating in Example 1 was omitted to form a metaloxide thin film on the substrate.

As a result of observation of the appearance of the surface of thesubstrate (surface on which the application liquid was spin coated) ofComparative Example 14, patchy scars were generated on the entiretyalthough the uniformity was found to some extent. Thus, a practicallyapplicable value as a substrate on which a metal oxide thin film wasformed was not accepted. Note that an electron micrograph of the surfaceof the thin film of Comparative Example 14 is shown in FIG. 9. The SEMphotograph reveals that fine cracks were generated.

Comparison of Example 1 with Comparative Example 14 verified thatformation of a compact and uniform metal oxide thin film on thesubstrate failed unless the primary heating and the secondary heatingwere not carried out sequentially at certain temperatures even if thesame application liquid was applied on the substrate.

(Influences of Water Content) COMPARATIVE EXAMPLE 15

Entirely similar operations to those in Example 1 were carried outexcept that the moisture content was set to be 0.03% by weight.Additionally, observation of the appearance and SEM photography similarto those in Example 1 were carried out. Although the observation of theappearance suggested that the surface was uniform to some extent, finecracks were confirmed to be generated on the whole surface when viewedon the SEM photograph. Note that an SEM photograph of the surface of thesubstrate (surface on which the application liquid was spin coated) ofComparative Example 15 is shown in FIG. 10.

Comparison of Example 1 with Comparative Example 15 verified thatformation of a compact and uniform metal oxide thin film on thesubstrate failed unless the moisture was contained in the applicationliquid.

From the description hereinabove, many modifications and otherembodiments of the present invention are apparent to persons skilled inthe art. Accordingly, the foregoing description should be construedmerely as an illustrative example, which was provided for the purpose ofteaching best modes for carrying out the present invention to personsskilled in the art. Details of the construction and/or function of thepresent invention can be substantially altered without departing fromthe spirit thereof.

INDUSTRIAL APPLICABILITY

The metal salt-containing composition, the substrate, the method formanufacturing the substrate of the present invention are useful in asemiconductor field and the like such as in manufacturing a substratehaving a coating film, a transparent electric conductive film, etc.

1. A metal salt-containing composition comprising a metal salt, apolyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and a solvent, wherein: the molar ratio of thepolyvalent carboxylic acid to the metal salt is not less than 0.5 andnot more than 4.0; the moisture content of the composition is not lessthan 0.05% by weight; and the composition is used for forming a metaloxide thin film by applying on a substrate followed by baking.
 2. Themetal salt-containing composition according to claim 1, wherein themetal salt is at least one salt selected from the group consisting ofMg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Nb, Ta, Cr, W, Fe, Ni, Cu, Ag, Zn, Al,Ga, In, Sn and Sb.
 3. The metal salt-containing composition according toclaim 1, wherein the metal salt is at least one metal salt selected fromthe group consisting of a nitric acid salt, a sulfuric acid salt, acarboxylic acid salt, a halide, an alkoxide and an acetyl acetone salt.4. The metal salt-containing composition according to claim 1, whereinthe polyvalent carboxylic acid is at least one selected from the groupconsisting of maleic acid, citraconic acid, phthalic acid andtrimellitic acid.
 5. The metal salt-containing composition according toclaim 1, wherein the content of the metal salt is not less than 0.005mol/L and not more than 1 mol/L.
 6. A substrate having a metal complexfilm formed on the surface thereof, the metal complex film beingobtained by: applying on the surface of the substrate a solutioncomprising a metal salt, a polyvalent carboxylic acid having a cis-formstructure of —C(COOH)═C(COOH)—, and a solvent, the molar ratio of thepolyvalent carboxylic acid to the metal salt being not less than 0.5 andnot more than 4.0, and the moisture content of the solution being notless than 0.05% by weight; and drying by heating at a temperature of notlower than 100° C. and not higher than 250° C.
 7. The substrateaccording to claim 6, wherein the metal salt is at least one saltselected from the group consisting of Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Nb,Ta, Cr, W, Fe, Ni, Cu, Ag, Zn, Al, Ga, In, Sn and Sb.
 8. The substrateaccording to claim 6, wherein the metal salt is at least one metal saltselected from the group consisting of a nitric acid salt, a sulfuricacid salt, a carboxylic acid salt, a halide, an alkoxide and an acetylacetone salt.
 9. The substrate according to claim 6, wherein thepolyvalent carboxylic acid is at least one selected from the groupconsisting of maleic acid, citraconic acid, phthalic acid andtrimellitic acid.
 10. The substrate according to claim 6, wherein thecontent of the metal salt is not less than 0.005 mol/L and not more than1 mol/L.
 11. A substrate having a metal oxide film formed on the surfacethereof obtained by further heating the substrate according to claim 6at a temperature of no lower than 400° C.
 12. A method for manufacturinga substrate having an oxidized metal thin film formed on the surfacethereof, the method comprising: an application step of applying on thesurface of the substrate a solution comprising a metal salt, apolyvalent carboxylic acid having a cis-form structure of—C(COOH)═C(COOH)—, and a solvent, the molar ratio of the polyvalentcarboxylic acid to the metal salt being not less than 0.5 and not morethan 4.0, and the moisture content of the solution being not less than0.05% by weight; a primary heating step of drying by heating thesolution at a temperature of not lower than 100° C. and not higher than250° C. ; and a secondary heating step of further heating the substrateafter the primary heating step at a temperature no lower than 400° C.13. The method for manufacturing a substrate according to claim 12,wherein the metal salt is at least one salt selected from the groupconsisting of Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Nb, Ta, Cr, W, Fe, Ni, Cu,Ag, Zn, Al, Ga, In, Sn and Sb.
 14. The method for manufacturing asubstrate according to claim 12, wherein the metal salt is at least onemetal salt selected from the group consisting of a nitric acid salt, asulfuric acid salt, a carboxylic acid salt, a halide, an alkoxide and anacetyl acetone salt.
 15. The method for manufacturing a substrateaccording to claim 12, wherein the polyvalent carboxylic acid is atleast one selected from the group consisting of maleic acid, citraconicacid, phthalic acid and trimellitic acid.
 16. The method formanufacturing a substrate according to claim 12, wherein the content ofthe metal salt in the solution is not less than 0.005 mol/L and not morethan 1 mol/L.